1. Field of the Invention
The present invention relates to a liquid crystal display (LCD).
2. Description of the Prior Art
With low prices and high quality of liquid crystal displays (LCDs), the LCD is widely applied in notebooks, PDAs, mobile phones, clocks and watches, digital video cameras, digital cameras, TVs, and so on. In general, an LCD comprises a display panel and a backlight unit. The backlight unit positioned under the display panel includes a light source and an optical film for uniformly providing light for the display panel. Consequently, the pixel units of the display panel are able to display images. Therein, a direct-type backlight unit having a light source directly under the display panel can be applied for high illumination requirement LCDs or large size LCDs, such as computer monitors or TV panels.
Referring to FIG. 1, it shows a sectional view of a prior art LCD 10. The prior art LCD 10 comprises a liquid crystal display panel 12 and a backlight unit 14 positioned under the liquid crystal display panel 12. The liquid crystal display panel 12 comprises a plurality of pixel units (not shown in FIG. 1), and the backlight unit 14 comprises a light source 16, an optical film 18 positioned between the light source 16 and the liquid crystal display panel 12, and a reflecting sheet 20 positioned under the light source and fixed on a housing 22. The light source 16 is used for illuminating light to the liquid crystal display panel 12, and the reflecting sheet 20 is used for reflecting the light generated by the light source 16 so as to improve the light utility rate and provide a better illumination. The optical film 18 includes a diffuser sheet 24, a prism sheet 26, diffuser sheet and a diffusion plate 28. The reflecting sheet 20 has a plurality of printing points 29 distributed on its surface for uniformly scattering the light generated by the light source 16 on the liquid crystal display panel 12. The diffusion plate 24 and the prism 26 are used for further modifying the difference of light intensity. Therefore, the liquid crystal display panel 12 can receive light with uniform intensity.
Following the tendency of high illumination, the light source 16 of the backlight unit 14 usually includes a plurality of cathode fluorescent tubes 17 assembled in a narrow, sealed space, and the heat generated by the cathode fluorescent tubes 17 does not disperse to outside. When the LCD 10 is operated for a long time, the temperature near the cathode fluorescent tubes 17 will arise excessively high, which affects functions of the LCD 10 and results in low display quality. Furthermore, the optical film 18 positioned adjacent to the light source 16 will easily become deformed, which results in a reduction of product life. When the LCD 10 integrated with wide visual angle technology is applied for TV products, the numbers and the electric currents of cathode fluorescent tubes 17 of the light source 16 are increased according to the present method for maintaining high illumination. However, the above-mentioned method also increases the heat generated by the light source 16, and the problem of heat dispersion of the backlight unit 14 gets worse.